Defense against infections related to the use of biological agents in acts of terrorism or war is a national priority. To achieve this end, new methods to detect, treat, and prevent infection with Category A-C pathogens must be developed. Treatment may include prevention of infection in the case of an immediate threat, protection of immunocompromised individuals, or post-exposure treatment to suppress infection and disease. Ideal agents for these applications would be stable, broad spectrum, fast acting, nontoxic towards human cells, inexpensive, and easy to manufacture. Conventional antibiotics meet some of these criteria, but both the rise in antibiotic resistant organisms and a dearth of new broad-based antibiotics make identification of new antimicrobials imperative. Granulysin is an alpha-helical protein expressed by human natural killer cells and activated T lymphocytes. Recombinant granulysin lyses both mammalian cells and a broad spectrum of microbes. Synthetic peptides (10-30 residues) corresponding to the central region of granulysin recapitulate its lytic activity. In a subset of these peptides, replacement of cysteine or arginine residues, or introduction of D-amino acids to disrupt the alpha-helix, results in the loss of activity against mammalian cells with little or no effect on antimicrobial activity. The goal of this Program is to develop novel immunotherapeutics based on these granulysin peptides. Additional derivatives will be generated in Project 1, evaluated in vitro and in vivo in Project 2, and characterized for mechanism of action in Project 3. These projects will be supported by three cores--synthesis/inventory; a BSL-3 facility, and administration. The information gleaned from these studies should lead to the development of new immunotherapeutics for biodefense and for treatment of antibiotic resistant pathogens.